(i) Field of the Invention
The present invention relates to a method for concentrating (purifying) a chlorine gas by the utilization of a pressure swing adsorption method (hereinafter referred to as "PSA method"), and particularly, it relates to a method and an apparatus for concentrating/purifying a chlorine containing gas so as to lower the chlorine concentration in a treated exhaust or residue gas and increase the purity of a (concentrated) chlorine gas product.
(ii) Description of the Related Art
As methods for concentrating a chlorine gas which have been heretofore known, there are a method which comprises absorbing the chlorine gas by a chlorine-containing organic solvent, and then vaporizing the chlorine gas; a method which comprises pressurizing/cooling a gas, and then separating the resultant liquid chlorine; a method which comprises adsorbing chlorine by silica gel (U.S. Pat. No. 1,617,305); and other techniques. However the method using a chlorine-containing solvent is not preferable, because the chlorine solvent has an influence on process parameters and hence the use of chlorine as a solvent will be restricted. On the other hand, the method which comprises pressurizing/cooling the chlorine gas to liquefy it requires a compressor and a freezer and therefore this method is not considered to be an advantageous technique. The method which comprises adsorbing chlorine by silica gel is also poor in efficiency and it is not an industrially effective technique. Therefore, this method has not been utilized so far. In particular, there have not been any industrially effective method and apparatus by which gases having low chlorine concentration can be converted to gases with a high concentration are concentrated without leaking the chlorine gas into an exhaust or residue gas.
As is apparent from the foregoing, a method and apparatus have not been developed thus far which provides an industrially effective process for concentrating/purifying a chlorine gas which contains impurities.
Furthermore, there has not existed a method for separating chlorine from a mixed gas containing the chlorine gas, particularly from a gas having a relatively low chlorine concentration and containing moisture to concentrate the chlorine.